1. Field of the Invention
The present invention relates to a semiconductor device used as an IC chip (hereinafter also referred to as an ID chip) that is capable of storing required data in a memory circuit or reading required data by a contactless means such as wireless communication. In particular, the invention relates to a semiconductor device used as an ID chip formed over an insulating substrate such as glass and plastic.
2. Description of the Related Art
With the development and improvement of computer technologies and image recognition technologies, data identification utilizing media such as bar codes has been widely used for identification of product data and the like. It is expected that a larger amount of data is to be identified in the future. On the other hand, data identification utilizing bar codes is disadvantageous in that a bar code reader is required to be in contact with bar codes, and the amount of data stored in bar codes cannot be increased so much. Therefore, contactless data identification and increase in the storage capacity of media are required.
In view of the foregoing, an ID chip using an IC has been developed in recent years. In the ID chip, required data is stored in a memory circuit of an IC chip and the data is read by a contactless means, generally by a wireless means. It is expected that practical application of such an ID chip allows commercial distribution to be simplified and reduced in cost while maintaining high security.
An identification system using an ID chip is briefly described with reference to FIG. 4. FIG. 4 is a schematic view showing an identification system for wirelessly obtaining identification data of a bag. An ID chip 401 storing specific identification data is mounted on or inside a bag 404. Radio waves are transmitted from an antenna unit 402 of an interrogator (also called a reader/writer) 403 to the ID chip 401. When receiving the radio waves, the ID chip 401 sends its own identification data back to the antenna unit 402. The antenna unit 402 transmits the received identification data to the interrogator 403, and the interrogator 403 determines the identification data. In this manner, the interrogator 403 can obtain the data of the bag 404. Such a system enables distribution management, tabulation, prevention of counterfeit goods, and the like.
The ID chip has, for example, a configuration shown in FIG. 2. A semiconductor device 200 used as an ID chip includes an antenna circuit 201, a rectification circuit 202, a stabilizing power supply circuit 203, an amplifier 208, a demodulation circuit 213, a logic circuit 209, a memory control circuit 212, a memory circuit 211, a logic circuit 207, an amplifier 206, and a modulation circuit 205. The antenna circuit 201 includes an antenna coil 301 and a tuning capacitor 302 (FIG. 3A). The rectification circuit 202 includes diodes 303 and 304, and a smoothing capacitor 305 (FIG. 3B).
The operation of such an ID chip is described hereinafter. An AC signal received by the antenna circuit 201 is half-wave rectified by the diodes 303 and 304, and then smoothed by the smoothing capacitor 305. The smoothed voltage, which has many ripples, is stabilized by the stabilizing power supply circuit 203, and the stabilized voltage is supplied to the demodulation circuit 213, the amplifier 206, the logic circuit 207, the amplifier 208, the logic circuit 209, the memory circuit 211, and the memory control circuit 212. Meanwhile, a signal received by the antenna circuit 201 is inputted as a clock signal to the logic circuit 209 through the amplifier 208. A signal inputted from the antenna 301 is demodulated in the demodulation circuit 213, and inputted as data to the logic circuit 209.
The data inputted to the logic circuit 209 is decoded. Since the interrogator encodes data by deformable mirror code, NRZ-L code or the like, the logic circuit 209 decodes the data. The decoded data is transmitted to the memory control circuit 212, thereby memory data stored in the memory circuit 211 is read. The memory circuit 211 is required to be a nonvolatile memory circuit such as a mask ROM, which is capable of storing data even when a power supply is turned off. The memory circuit 211 stores, for example, 16-byte data having 4-byte family code, 4-byte application code, and two kinds of 4-byte user code set by users (see FIG. 12A).
The frequency of a transmitted and received signal is 125 kHz, 13.56 MHz, 915 MHz, or 2.45 GHz each having an ISO standard and the like. In addition, modulation and demodulation systems for transmitting and receiving signals are also standardized. An example of such an ID chip is disclosed in Patent Document 1.
[Patent Document 1] Japanese Patent Laid-Open No. 2001-250393
The aforementioned conventional semiconductor device for an ID chip has the following problems. In the case of a mask ROM being used as a memory circuit, data cannot be written except in the manufacture of a chip. Thus, an ID chip where data can be written except in the manufacture of the chip is required.
Meanwhile, in the case of an EEPROM being used as a memory circuit, user can rewrite data freely. However, at the same time, anyone other than the user can change data for identification that is not to be rewritten, which allows counterfeiting. Thus, an ID chip where data can be written only once is required to prevent such counterfeiting.